fix: add sample app for rendering cat images

Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com>

samples/mostly-adequate/chapter06_exampleapplication_test.go

@@ -0,0 +1,115 @@
+// Copyright (c) 2023 IBM Corp.
+// All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package mostlyadequate
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"regexp"
+
+	A "github.com/IBM/fp-go/array"
+	E "github.com/IBM/fp-go/either"
+	F "github.com/IBM/fp-go/function"
+	J "github.com/IBM/fp-go/json"
+	S "github.com/IBM/fp-go/string"
+
+	R "github.com/IBM/fp-go/context/readerioeither"
+	H "github.com/IBM/fp-go/context/readerioeither/http"
+)
+
+type (
+	FlickrMedia struct {
+		Link string `json:"m"`
+	}
+
+	FlickrItem struct {
+		Media FlickrMedia `json:"media"`
+	}
+
+	FlickrFeed struct {
+		Items []FlickrItem `json:"items"`
+	}
+)
+
+func (f FlickrMedia) getLink() string {
+	return f.Link
+}
+
+func (f FlickrItem) getMedia() FlickrMedia {
+	return f.Media
+}
+
+func (f FlickrFeed) getItems() []FlickrItem {
+	return f.Items
+}
+
+func Example_application() {
+	// pure
+	host := "api.flickr.com"
+	path := "/services/feeds/photos_public.gne"
+	query := S.Format[string]("?tags=%s&format=json&jsoncallback=?")
+	url := F.Flow2(
+		query,
+		S.Format[string](fmt.Sprintf("https://%s%s%%s", host, path)),
+	)
+	// flick returns jsonP, we extract the JSON body, this is handled by jquery in the original code
+	sanitizeJsonP := Replace(regexp.MustCompile(`(?s)^\s*\((.*)\)\s*$`))("$1")
+	// parse jsonP
+	parseJsonP := F.Flow3(
+		sanitizeJsonP,
+		S.ToBytes,
+		J.Unmarshal[FlickrFeed],
+	)
+	// markup
+	img := S.Format[string]("<img src='%s'/>")
+	// lenses
+	mediaUrl := F.Flow2(
+		FlickrItem.getMedia,
+		FlickrMedia.getLink,
+	)
+	mediaUrls := F.Flow2(
+		FlickrFeed.getItems,
+		A.Map(mediaUrl),
+	)
+	images := F.Flow2(
+		mediaUrls,
+		A.Map(img),
+	)
+
+	client := H.MakeClient(http.DefaultClient)
+
+	// func(string) R.ReaderIOEither[[]string]
+	app := F.Flow5(
+		url,
+		H.MakeGetRequest,
+		H.ReadText(client),
+		R.ChainEitherK(parseJsonP),
+		R.Map(images),
+	)
+
+	// R.ReaderIOEither[[]string]
+	// this is the managed effect that can be called to download and render the images
+	catImageEffect := app("cats")
+
+	// impure, actually executes the effect
+	catImages := catImageEffect(context.TODO())()
+	fmt.Println(E.IsRight(catImages))
+
+	// Output:
+	// true
+
+}